This project is designed to provide information on the mechanisms operating within reflex systems in the adult cat spinal cord, which include alpha motoneurons as the output link, as well as on the interconnections and interactions between reflex pathways and control systems descending to the spinal cord from supraspinal centers. Particular consideration is also given to interrelations between synaptic organization, intrinsic neuronal properties, and dynamic behavior of the alpha motoneurons, and the motor unit type, as defined by the physiological characteristics of the innervated muscle fibers. A variety of preparations have been used, including anesthetized, decerebrate animals as well as intact, freely moving cats. Electrophysiological and morphological data are obtained.